Mo-Si-B alloys for ultra-high temperature space and ground applications: liquid assisted fabrication under various temperature and time conditions

TL;DR

This study introduces a pressure-less reactive melt infiltration method to fabricate Mo-Si-B alloys, analyzing how temperature and time influence the microstructure and phase formation for ultra-high temperature applications.

Contribution

It presents a novel fabrication approach for Mo-Si-B alloys via melt infiltration, detailing the effects of processing conditions on microstructure and phase development.

Findings

Thicker reaction layers form at higher temperatures and longer times.

Phase composition includes MoSi2, Mo5Si3, and boron-rich interlayers.

Microstructure varies with temperature and duration of melt interaction.

Abstract

Boron-doped molybdenum silicides have been already recognized as attractive candidates for space and ground ultra-high temperature applications far beyond limits of state-of-the-art nickel based superalloys. In this work, we are exploring a new method for fabricating Mo-Si-B alloys (as coatings or small bulk components) by utilizing a pressure-less reactive melt infiltration approach. The basic assumption of this approach is a synthesis of binary and/or ternary and complex intermetallic phases (silicides, borides, borosilicides), through a direct interaction of Si-B melt with molybdenum . The main purpose of this work, was to examine the effect of temperature and time of Si-B melt interaction on the structure and morphology of the formed reaction products. For this purpose, sessile drop experiments were carried out on the eutectic Si-3.2B (wt%) alloy/Mo couples at temperature varying between 1385-1550{\deg}C and holding time between 10 to 30 minutes. The solidified sessile drop couples were subjected to microstructural characterization by means of light microscopy and scanning electron microscopy analyses performed both at "top-view" and cross-sectioned interfaces. The phases formed within the interaction zone were identified by using TEM/SAED and XRD techniques. It was documented that a thickness of both main product layer (MoSi2+Mo5Si3), as well as boron-rich interlayer increases with raising temperature and time of the Si-B melt interaction with Mo substrates.